class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int m = obstacleGrid.size(), n = obstacleGrid[0].size();
        //如果在起点或终点出现了障碍，直接返回0
        if (obstacleGrid[m - 1][n - 1] == 1 || obstacleGrid[0][0] == 1) 
            return 0;
        vector<vector<int>> dp (m, vector<int>(n, 0));
        // 初始化动规数组
        for(int i = 0; i < m && obstacleGrid[i][0] == 0; ++i)
            dp[i][0] = 1;
        for(int j = 0; j < n && obstacleGrid[0][j] == 0; ++j) 
            dp[0][j] = 1;

        for(int i = 1; i < m; ++i){
            for(int j = 1; j < n; ++j){
                // 如果没有障碍
                if(obstacleGrid[i][j] == 0)
                    dp[i][j] = dp[i-1][j]+dp[i][j-1];
            }
        }
        return dp[m-1][n-1];
    }
};